You had me going there with the title of the post, because there is a yardlong bean (Vigna unguiculata) with the varietal name "Taiwan Black". However, it is green podded, with black seeds.

The bean you describe sounds like one of the purple-podded yardlong beans, such as "Chinese Red Noodle". I have two purple-podded cultivars of V. unguiculata, both of which have either brown, or brown & white seeds. Since yardlong beans are often eaten stir fried, that is most likely what you have.

I hope you will be able to post photos, when the seeds are dry.